/**
 * express.js 中间件示例
 */

//导入Express模块
const express = require("express");
//创建Express应用
const app = express();
const router = express.Router();
//Express http服务端口
const port = 3001;

//内置中间件
app.use(express.static("public"));
app.use("/public", express.static("public"));
//解析json数据
app.use(express.json());
//url解析
app.use(express.urlencoded({extended: false}));





//应用层中间件 app.use()
//未定义路由路径的中间件,应用每次收到请求时执行该回调函数
app.use(function(req, res, next){
    console.log(`应用层中间件: Url-${req.url}, Time-${new Date().toLocaleString()}`);
    next();
});

//可在应用层中间件中定义路径,实际上响应指定路径上的任意类型的http请求
app.use("/mw/:id", function(req,res,next){
    console.log(`指定路径的应用层中间件,http请求:${req.method}`);
    next();
});

//路由层中间件,支持路由和中间件
router.use(function (req, res, next) {
    console.log(`路由层中间件: Url-${req.url}, Time-${new Date().toLocaleString()}`);
    next();
})

router.get("/router_mw/:id",function(req,res){
    console.log(`路由层中间件,路由参数:${req.params.id}`);
    res.send("渲染")
});

//使用路由层中间件
app.use(router);

//错误处理中间件
app.get("/test-error", function(){
    throw new Error("Oops!");
});

app.use(function(err,req,res,next){
    console.error(err.message);
    res.status(500).send("服务器500错误!");
});

app.use("*", function(req, res){
    console.log("404 Not found");
    res.json({
        status:404,
        title:"页面不存在"
    });
});



//启动Express服务
app.listen(port, function () {
    console.log(`MyApp访问地址:http://127.0.0.1:${port}`);
});